Composite phosphor powder, light emitting device using the same and method for manufacturing composite phoshpor powder

ABSTRACT

The invention provides a high quality composite phosphor powder which ensures diversity in emission spectrum, color reproduction index, color temperature and color, a light emitting device using the same and a method for manufacturing the composite phosphor powder. The composite phosphor powder comprises composite particles. Each of the composite particles includes at least two types of phosphor particles and a light transmitting binder. The phosphor particles have different emission spectrums. In addition, the light transmitting binder is formed between the phosphor particles and binds them together.

RELATED APPLICATION

This application claims the benefit of Korean Patent Application No.2005-77399 filed on Aug. 23, 2005 in the Korean Intellectual PropertyOffice, the disclosure of which is incorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a phosphor powder, and moreparticularly, a composite phosphor powder which emits light in a varietyof spectrums and produces color temperature, color reproduction indexand color precisely tailored to needs.

2. Description of the Related Art

A phosphor is utilized in a wide range of light emitting devices such asa light emitting diode device. The phosphor converts various excitationenergies such as photon, electron, heat and electric field into visiblelight. In order to obtain a desired emission wavelength, an adequateactivator ion and a matrix material are synthesized to manufacture aphosphor. An excitation energy transferred through a matrix of thephosphor to the active ion is converted to visible light, therebyemitting light. Here, the emission wavelength is determined bycombination of a given matrix and an activator doped therein. As aresult, the phosphor carries its own emission wavelength and accordinglyis extremely limited in altering the emission wavelength as desired.

FIG. 1 illustrates a spectrum of a conventional red phosphor and FIG. 2illustrates a spectrum of a conventional green phosphor. FIG. 1 is agraph illustrating an emission spectrum of SrS:Eu phosphor which is ared phosphor. FIG. 2 is a graph illustrating an emission spectrum ofSrGa₂S₄:Eu phosphor which is a green phosphor. As shown in FIGS. 1 and2, the phosphors each emit light in a specified wavelength range. Asjust described, only one type of phosphor fails to produce a variety ofcolors and emission spectrums, and moreover extremely limited types ofthe phosphors emit light at a desired wavelength.

In a method to overcome this problem, several types of phosphors havebeen mixed together. For example, in a light emitting device having anLED element (LED chip) mounted thereon, several types of phosphors aremixed to emit light in a broad wavelength range (e.g., white lightemission). FIG. 3 illustrates an example thereof.

Referring to FIG. 3, a light emitting device 10 includes a blue LED chip18 mounted in a recess of a housing 11. Terminal electrodes 12 areconnected to the LED chip via bonding wires 19. Over the LED chip 18, afirst phosphor (e.g., a red phosphor) 13 and a second phosphor (e.g., agreen phosphor) 14 are mixed in a molding resin 15 such as epoxy.However, owing to density differences between the first phosphor 13 andthe second phosphor 14, the phosphor of high density (the secondphosphor) sinks and the phosphor of low density (the first phosphor)floats (a layering phenomenon). This fails to produce color reproductionindex and emission spectrum as originally designed or expected,resulting in uneven color.

SUMMARY OF THE INVENTION

The present invention has been made to solve the foregoing problems ofthe prior art and therefore an object according to certain embodimentsof the present invention is to provide a composite phosphor powder whichemits light at a variety of spectrums and precisely ensures diversity incolor temperature, color and color reproduction index.

Another object according to certain embodiments of the invention is toprovide a method for manufacturing a composite phosphor powder whichemits light in a variety of spectrums and precisely ensures diversity incolor temperature, color and color reproduction index.

Further another object according to certain embodiments of the inventionis to provide a light emitting device which employs a composite phosphorpowder to precisely ensure diversity in emission spectrum, colortemperature, color and color reproduction index.

According to an aspect of the invention for realizing the object, thereis provided a composite phosphor powder comprising composite particles,wherein each of the composite particles comprises at least two types ofphosphor particles having different emission spectrums and a lighttransmitting binder for binding the phosphor particles, the lighttransmitting binder formed between the phosphor particles.

According to an embodiment of the invention, the phosphor particles ofthe each composite particle have different peak emission wavelengths.

This allows the composite phosphor powder to exhibit emission spectrumspeculiar to each of the phosphor particles, and other new broaderemission spectrums. Also, the emission spectrums can be adjusted byvarying relative contents of the phosphor particles comprising thecomposite particles.

According to an embodiment of the invention, the light transmittingbinder comprises a light transmitting polymer resin. Preferably, thelight transmitting binder comprises an epoxy resin or a silicone resin.The light transmitting binder binds the phosphor particles together intoa composite particle.

Preferably, the composite phosphor particles have a mean diameter of 10to 100 μm. More preferably, the composite phosphor particles have a meandiameter of 20 to 50 μm. Preferably, to obtain uniform color of lightemitted, the composite particles are uniformly sized.

According to an embodiment of the invention, the each composite particleincludes a red phosphor and a green phosphor. For example, the eachcomposite particle comprises SrS:Eu and SrGa₂S₄:Eu at a various ratio.

According to another embodiment of the invention, the each compositeparticle includes a green phosphor and a yellow phosphor. For example,the each composite particle comprises SrGa₂S₄:Eu and YAG:Ce at a variousratio.

According to further another embodiment of the invention, the eachcomposite particle includes a red phosphor, a green phosphor and ayellow phosphor. For example, the each composite particle comprisesSrS:Eu, SrGa₂S₄:Eu and YAG:Ce at a various ratio.

According to still another embodiment of the invention, the eachcomposite particle comprises a red phosphor, a green phosphor, a yellowphosphor and an orange phosphor. For example, the each compositeparticle comprises SrS:Eu, SrGa₂S₄:Eu, YAG:Ce and ZnSeS:Cu at a variousratio.

According to another aspect of the invention for realizing the object,there is provided a method for manufacturing a composite phosphorpowder, comprising steps of:

mixing at least two types of phosphor particles with a lighttransmitting binder to form a precursor of a composite phosphor;

mixing a dispersion medium added with a surfactant with the precursorand stirring the mixture to form stabilized unit particles of thecomposite phosphor within the dispersion medium; and

heating the dispersion medium to cure the light transmitting binder,thereby solidifying composite phosphor particles.

Preferably, the light transmitting binder comprises an epoxy resin or asilicone resin. Preferably, the dispersion medium comprises distilledwater. In this case, a water hardening agent is added to the precursor.Also, the surfactant may comprise Poly Acryl Amide (PAA). Alternatively,the dispersion medium comprises alcohol such as ethyl alcohol.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other objects, features and other advantages of thepresent invention will be more clearly understood from the followingdetailed description taken in conjunction with the accompanyingdrawings, in which:

FIG. 1 is a graph illustrating an emission spectrum of a conventionalred phosphor;

FIG. 2 is a graph illustrating an emission spectrum of a conventionalgreen phosphor;

FIG. 3 is a cross-sectional view illustrating a conventional lightemitting device using phosphor mixtures;

FIG. 4 is a schematic view illustrating a composite phosphor particleaccording to an embodiment of the invention;

FIG. 5 is a schematic view illustrating a composite phosphor particleaccording to another embodiment of the invention;

FIGS. 6 to 11 are graphs illustrating emission spectrums of compositephosphor powders according to various embodiments of the invention;

FIG. 12 is a SEM picture illustrating composite phosphor particlesaccording to an embodiment of the invention; and

FIG. 13 is a cross-sectional view illustrating a light emitting deviceusing a composite phosphor powder according to still another embodimentof the invention

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

Preferred embodiments of the present invention will now be described indetail with reference to the accompanying drawings. It is intended,however, that the embodiments shall be interpreted as illustrative only,but various variations and modifications can be made without departingfrom the scope of the invention.

FIG. 4 is a schematic view illustrating a composite phosphor particleaccording to an embodiment of the invention. A composite phosphor powderis comprised of composite phosphor particles. Referring to FIG. 4, acomposite particle containing phosphors, i.e., the composite phosphorparticle 50 contains two different types of phosphors 53 and 55, whichdiffer in the emission spectrum. Preferably, the phosphors 53 and 55 ofthe composite phosphor particle 50 exhibit different peak emissionwavelengths. Also, a light transmitting binder 51 is formed between thephosphors 53 and 55 to bind them together. The light transmitting binder51 may adopt a light transmitting polymer resin such as an epoxy resinor a silicone resin.

The phosphors 53 and 55 can be contained at an adjustable ratiodepending on needs. In this fashion, two types of phosphors havingdifferent emission spectrums are combined at a various ratio into acomposite particle, thereby achieving uniformity in color and diversityin emission spectrum, color reproduction index and color temperature.The two phosphors 53 and 55 are exemplified by a red phosphor and agreen phosphor. Alternatively, the phosphors 53 and 55 may adopt a greenphosphor and a yellow phosphor.

The composite phosphor particle 50 has a mean diameter of 10 to 100 μm,preferably 20 to 50 μm. Preferably, composite phosphor particles 50within the composite phosphor powder have a uniform diameter D overall.This is because the uniformly sized composite particles more contributeto uniform color. According to the invention, individual phosphorscontained in the composite phosphor particle are not limited to only twotypes. Optionally at least three types of phosphors are contained at avarious ratio in the composite phosphor particle.

FIG. 5 is a schematic view illustrating a composite phosphor particleaccording to another embodiment of the invention. Referring to FIG. 5,the composite phosphor particle 60 includes a light transmitting binder61 such as an epoxy resin and three different types of phosphorparticles 63, 64 and 65 bound thereby. The phosphors 63, 64 and 65feature different emission spectrums (preferably different peak emissionwavelengths). For example, the phosphors 63, 64 and 65 may adopt a redphosphor, a green phosphor and a yellow phosphor. A composite phosphorpowder comprised of composite phosphor particles produces visible lightof a broad wavelength range, and ensures diversity in emission spectrum,color temperatures, color reproduction index and color. Especially, thisprevents incidence of a layering phenomenon as in the prior art, therebyproducing more uniform color and the emission spectrum precisely asdesigned.

FIGS. 6 to 11 are graphs illustrating emission spectrums of compositephosphor powders according to various embodiments of the invention. Thecomposite phosphor powders whose spectrums are plotted in FIGS. 6 to 11employ an epoxy resin as a light transmitting binder.

First, FIG. 6 depicts an emission spectrum of a composite phosphorpowder having a composition expressed by 80% SrS:Eu and 20% SrGa₂S₄:Eu,which contains a red phosphor of SrS:Eu and a green phosphor ofSrGa₂S₄:Eu at a ratio of 80% and 20%. As shown in FIG. 6, the compositephosphor powder exhibits a new spectrum of a broader wavelength comparedto a spectrum (refer to FIGS. 1 and 3) of a conventional individualphosphor. The emission spectrum can be adjusted by varying a contentratio of the phosphors.

FIG. 7 depicts an emission spectrum of a composite phosphor powderhaving a composition expressed by 50% SrS:Eu and 50% SrGa₂S₄:Eu, whichcontains a red phosphor and a green phosphor. As apparent from thespectrums of FIGS. 6 and 7, even in a case where individual phosphors ofthe same type are used, an emission spectrum of the composite phosphorpowder is varied by a content ratio. Therefore, variation in the contentratio leads to diversity in the emission spectrum.

FIG. 8 represents an emission spectrum of a composite phosphor powderhaving a composition expressed by 40% SrS:Eu, 40% SrGa₂S₄:Eu and 20%YAG:Ce, which contains a red phosphor, a green phosphor and a yellowphosphor. As shown in FIG. 8, the composite phosphor powder emitsvisible light of high intensity at a wavelength ranging from 500 to 650nm.

FIG. 9 represents an emission spectrum of a composite phosphor powderhaving a composition expressed by 30% SrS:Eu, 30% SrGa₂S₄:Eu and40%YAG:Ce, which contains a red phosphor, a green phosphor and a yellowphosphor. As shown in FIGS. 8 and 9, the content ratio of the phosphorsis varied to adjust the emission spectrum thereof. Therefore,adjustability of the content ratio of the phosphors allows the emissionspectrum to be designed diversely.

FIG. 10 depicts an emission spectrum of a composite phosphor powderhaving a composition expressed by 35% SrS:Eu, 35% SrGa₂S₄:Eu, 15%YAG:Ce, and 15% ZnSeS:Cu, which contains a red phosphor, a greenphosphor, a yellow phosphor and an orange phosphor. As shown in FIG. 10,very high and uniform emission intensity is plotted at a wavelength of540 to 610 nm. In this fashion, the number of the phosphor types isincreased to produce more various types of emission spectrums in a broadwavelength range.

FIG. 11 depicts an emission spectrum of a composite phosphor powderhaving a composition expressed by 50% SrGa₂S₄:Eu and 50% YAG:Ce, whichcontains a green phosphor and a yellow phosphor. As shown in FIG. 11,the spectrum of the composite phosphor powder exhibits a peak emissionwavelength in a yellow-green area. FIG. 12 is a SEM picture illustratingparticles of a composite phosphor having a composition expressed by 50%SrGa₂S₄:Eu and 50% YAG:Ce, which carries the spectrum of FIG. 11. Asshown in FIG. 12, individual phosphors contained in the compositephosphor particle prevent occurrence of a layering phenomenon as in theprior art (refer to FIG. 3).

As apparent from the emission spectrum of the composite phosphor powdersaccording to the various embodiments, the invention ensures diversity inemission spectrum and accordingly in color reproduction index, colortemperature and color. Furthermore, according to the invention, alayering phenomenon (refer to FIG. 3) as in the prior art does not takeplace so that a designed emission spectrum can be precisely achieved.

A method for manufacturing a composite phosphor powder will be explainedhereunder according to an embodiment of the invention.

First, at least two types of phosphor particles and a light transmittingbinder are mixed together to form a precursor of a composite phosphor.For example, a green phosphor of SrGa₂S₄:Eu and a yellow phosphor ofYAG:Ce are mixed with an epoxy used as a filler to obtain the precursor(precursor of the composite phosphor). Alternatively, alkoxide used as awater hardening agent may be added to be mixed together.

Next, a surfactant of Poly Acril Amide (PAA) is mixed in distilled waterto produce a dispersion medium, which is then mixed with the precursor.When the dispersion medium mixed with the precursor is stirred, thesurfactant sticks onto an interface between epoxy binding the phosphorstogether and distilled water. This produces stabilized unit particles ofthe composite phosphor (including phosphor particles of SrGa₂S₄:Eu andYAG:Ce and epoxy filled therebetween)

Thereafter, the dispersion medium is heated to about 100° C. to remove asolvent (distilled water) and cure epoxy. This solidifies the compositephosphor particles. The composite phosphor particles include thephosphors of SrGa₂S₄:Eu and YAG:Ce and the epoxy binding them together.The composite phosphor powder is comprised of the composite phosphorparticles.

In this embodiment, epoxy is employed as a light transmitting binder buta silicone resin may be substituted therefor. Also, in this embodiment,distilled water is employed as a dispersion medium for dispersing theprecursor but alcohol may be substituted therefor. The compositephosphor powder obtained thereby is combinable with an LED chip toeasily manufacture a light emitting device.

FIG. 13 is a cross-sectional view illustrating an exemplary lightemitting device using a composite phosphor powder according to theinvention. Referring to FIG. 13, in the light emitting device 100, anLED chip 108 is mounted in a recess of a housing 101. A side of therecess of the housing 101 serves as a reflecting surface. Terminalelectrodes 102 disposed in the housing 101 are connected to the LED chip108 via bonding wires 109. A molding resin 105 for encapsulating the LEDchip 108 has composite phosphor particles A dispersed therein. As shownin FIG. 13, all the composite phosphor particles A are similarly dense,thereby preventing incidence of a layering phenomenon as in the priorart. Accordingly, uniform and precise color is produced.

The composite phosphor powder of preferred embodiments of the inventioncan be advantageously employed in a white light emitting device usingthe LED chip. For example, the composite phosphor powder of theinvention is applicable to an LED package device capable of achievingcolor reproduction index and color temperature which approximate naturalwhite light.

As set forth above, according to preferred embodiments of the invention,a composite phosphor powder employed emits light in a variety ofspectrums and precisely ensures diversity in color temperature, colorand color reproduction index. Especially, the composite phosphor powdercan be applied to an LED device, thereby producing light with variouscolor temperatures and color reproduction indexes, which includes whitelight or polychromatic light of other wavelengths.

While the present invention has been shown and described in connectionwith the preferred embodiments, it will be apparent to those skilled inthe art that modifications and variations can be made without departingfrom the spirit and scope of the invention as defined by the appendedclaims.

1. A composite phosphor powder comprising composite particles, whereineach of the composite particles comprises at least two types of phosphorparticles having different emission spectrums and a light transmittingbinder for binding the phosphor particles, the light transmitting binderformed between the phosphor particles.
 2. The composite phosphor powderaccording to claim 1, wherein the at least two types of phosphorparticles have different peak emission wavelengths.
 3. The compositephosphor powder according to claim 1, wherein the light transmittingbinder comprises a light transmitting polymer resin.
 4. The compositephosphor powder according to claim 3, wherein the light transmittingbinder comprises an epoxy resin or a silicone resin.
 5. The compositephosphor powder according to claim 1, wherein the composite phosphorparticles have a mean diameter of 10 to 100 μm.
 6. The compositephosphor powder according to claim 1, wherein the composite phosphorparticles have a mean diameter of 20 to 50 μm.
 7. The composite phosphorpowder according to claim 1, wherein the each composite particleincludes a red phosphor and a green phosphor.
 8. The composite phosphorpowder according to claim 7, wherein the each composite particlecomprises SrS:Eu and SrGa₂S₄:Eu.
 9. The composite phosphor powderaccording to claim 1, wherein the each composite particle includes agreen phosphor and a yellow phosphor.
 10. The composite phosphor powderaccording to claim 9, wherein the each composite particle comprisesSrGa₂S₄:Eu and YAG:Ce.
 11. The composite phosphor powder according toclaim 1, wherein the each composite particle includes a red phosphor, agreen phosphor and a yellow phosphor.
 12. The composite phosphor powderaccording to claim 11, wherein the each composite particle eachcomprises SrS:Eu, SrGa₂S₄:Eu and YAG:Ce.
 13. The composite phosphorpowder according to claim 1, wherein the each composite particlecomprises a red phosphor, a green phosphor, a yellow phosphor and anorange phosphor.
 14. The composite phosphor powder according to claim13, wherein the each composite particle comprises SrS:Eu, SrGa₂S₄:Eu,YAG:Ce, and ZnSeS:Cu.
 15. A method for manufacturing a compositephosphor powder, comprising steps of: mixing at least two types ofphosphor particles with a light transmitting binder to form a precursorof a composite phosphor; mixing a dispersion medium added with asurfactant with the precursor and stirring the mixture to formstabilized unit particles of the composite phosphor within thedispersion medium; and heating the dispersion medium to cure the lighttransmitting binder, thereby solidifying composite phosphor particles.16. The method according to claim 15, wherein the light transmittingbinder comprises an epoxy resin or a silicone resin.
 17. The methodaccording to claim 15, wherein the dispersion medium comprises distilledwater.
 18. The method according to claim 17, wherein a water hardeningagent is added to the precursor.
 19. The method according to claim 17,wherein the surfactant comprises Poly Acryl Amide (PAA).
 20. The methodaccording to claim 15, wherein the dispersion medium comprises alcohol.21. A light emitting device comprising: a light emitting diode chip; amolding resin for encapsulating the light emitting diode chip; and acomposite phosphor powder dispersed within the molding resin, thecomposite phosphor powder comprising composite particles, wherein eachof the composite particles comprises at least two types of phosphorparticles having different emission spectrums and a light transmittingbinder for binding the phosphor particles, the light transmitting binderformed between the phosphor particles.
 22. The light emitting deviceaccording to claim 21, further comprising a housing having a recess forseating the light emitting diode chip therein.